1. FIELD OF THE INVENTION
The invention relates to a linear motor with a cylinder containing an axially movable piston to which a piston rod extending through at least one of the end faces of the cylinder is fitted, the section of the piston rod which is outside the cylinder being secured against torsion by being fixed to a co-moving torsion protection element movable in the axial direction of the cylinder in conjunction with a sliding guide fixed thereto.
2. DESCRIPTION OF THE PRIOR ART
Linear motors of this type are generally known, for instance from DE-GM No. 85 05 017, and used for the linear displacement of a power take-off device linked to the piston rod outside the cylinder. The linear motor is actuated by suitable pressurisation, for instance by admitting air to the cylinder operating spaces separated by the piston. By securing the piston rod against torsion, i.e. rotation in relation to the cylinder, the power take-off device can be precisely positioned, which is vital in such fields as handling or robotics. Known linear motors are usually provided for this purpose with a rod extending parallel to the piston rod and connected thereto by means of a carrier, this rod being guided in a sliding guide in the shape of an eye provided on the cylinder. The axial dimension of the sliding guide is relatively short, leading to inadequate precision of the torsion protection element, especially in the extended position of the piston rod. This is particularly noticeable if the piston rod is subjected to torque by way of the power take-off device. This arrangement further requires expensive additional external measures to support the piston rod when displacing heavy weights, since known torsion protection devices are not suitable for supporting functions of this kind. The insufficient torsional rigidity of the known torsion protection device further makes the accurate positioning of the power take-off device virtually impossible.